Study assessments for Crohn's disease will be performed every 12 weeks through Week 108. At week 12, the investigator will make a determination of whether the subject is receiving clinical benefit, and subjects who are not receiving clinical benefit must be withdrawn. More frequent blood draws are required for liver function testing only; every 2 weeks for the first 12 weeks, then every 4 weeks up to Week 52, and every 12 weeks after Week 60 for the duration of the study.